To prepare mushrooms, you must always remember not to wash them as they will absorb moisture and this will affect the taste and make them soggy.
Instead, take a damp cloth (or kichen paper) and wipe each mushroom clean. It's also worth noting that they don't need to be peeled as the skin holds essential flavour and nutrients. The stalks are useful too.
However those of the Shitake mushroom are quite often chewy and should be completely removed from the mushroom's cap. Cut mushrooms or leave them whole, as indicated by the recipe.